Fluorescent 3D printed microstructures could thwart counterfeit money

Nov 16, 2017 | By Benedict

Researchers at the Karlsruhe Institute of Technology and optical company ZEISS are using fluorescent 3D printed microstructures to improve counterfeit protection. The innovation could prevent the forgery of bank notes, documents, and branded products.

When you hear about 3D printing and security, the news often concerns clever makers finding ways to crack established security systems. Just this week, for example, we saw how a security firm used a 3D printed mask to crack into the iPhone X’s Face ID system.

Occasionally, however, 3D printing simply gets used to protect or improve security systems, and a new innovation from Germany’s Karlsruhe Institute of Technology (KIT) and ZEISS aims to protect one of the most important pillars of society: money.

The researchers think their new 3D microstructure technique could be one of the best methods yet of ensuring authenticity in money, documents, and commercial products. And all it takes it switching from a 2D approach to a 3D one.

“Today, optical security features such as holograms are frequently based on two-dimensional microstructures,” explained Professor Martin Wegener, a 3D printing expert at KIT’s Institute of Nanotechnology. "By using 3D printed fluorescent microstructures, counterfeit protection can be increased.”

These 3D printed fluorescent microstructures measure only around 100 µm in length, and are virtually invisible to the naked eye. But despite their size, they have proved to be extremely effective.

The 3D printed microstructures are made up into a cross-grid scaffold structure, with variously colored fluorescent dots placed throughout.

It’s not a system you can easily reel off on your desktop FDM 3D printer. Rather, the researchers used a laser lithography printer from Nanoscribe, a spinoff of KIT, to print either voluminous structures with an edge length of just a few millimeters or microstructured surfaces spanning a few square centimeters in size.

The secret to producing the tiny fluorescent dots throughout the scaffold is an acrylate-based photoresist containing CdSSe-based core–shell semiconductor quantum dots. By using this resist in the 3D printing process, the researchers can embed the filigree structure within a transparent polymer, protecting it against damage.

These tiny 3D printed security to features could be embedded into the transparent windows of bank notes, and could even be put into security tags to protect things like pharmaceuticals, car spare parts, and mobile accumulators from counterfeiting.

Special scanning devices would be used to read the 3D printed microstructures at, for example, a cash desk.

“Security features produced in this way are not only of individual character, but also very complex in manufacture,” said KIT’s Frederik Mayer. “This makes life difficult to forgers.”

The researchers’ full study, “3D Fluorescence-Based Security Features by 3D Laser Lithography,” can be found here. Its other authors were Stefan Richter, Philipp Hübner, and Toufic Jabbour.